1. Field of the Invention
Rolling bearings have been used for many rotating systems due to their low friction, high rigidity and ability to support a combination of radial and thrust loading. The performance of the bearing assembly and its lubrication system are instrumental in increasing the maximum speed of the rotating system.
A good lubrication system not only can increase the rotating speed and prolong the service life of a bearing assembly, but also has a considerable advantage in reducing the power consumption of the entire system. There are at present several lubrication systems used for rolling bearings, such as grease, oil mist, oil air, and oil jet, etc. The grease lubrication, due to its poor heat transfer capability, is only applied to the rolling bearings operated at a low to medium rotating speed. The heat dissipation of the bearings for use in a high-speed rotation system is an important factor to consider. A suitable lubrication system for high speed operation, such as oil mist, oil air, and oil jet, must be capable of providing the bearings with adequate lubrication and cooling. In these systems, the operating parameters, such as the amount of oil supply, the flow rate of air, and the number of nozzles, have significant effects on the performance of rolling bearings.
An appropriate preload applied to the rolling bearings can eliminate the clearance between the rolling elements and the inner and outer races, and thus increases the rigidity of the rotating spindle. The preload can also reduce the sliding to rolling ratio so that the temperature rise and wear by friction produced due to excessive sliding are able to be prevented. However, a large preload may cause too heavy a load on the bearings, and thus adversely affect the fatigue life, temperature rise and power consumption of the bearings. Therefore, the ability to control the preload (axial load) applied to the rolling bearings within an appropriate range while maintaining a high speed rotation and a long service life for the rolling bearings is an important issue.
2. Description of the Prior Art
Evaluating the performance of rolling bearings is generally done by measuring the following parameters: the friction torque, temperature rise, vibration frequency, and vibration amplitude, etc. These parameters will change as the operation conditions, such as the rotating speed, load and lubrication, of the bearings change. Therefore, the performance testing for the bearings must regulate these conditions. There are many methods at present for measuring these parameters. Typical examples can be found in U.S. Pat. Nos. 3,952,566; 4,729,239; 4,763,508; 5,031,443; 5,184,505; 5,226,308; and 5,477,730.
Some systems disclosed in the above-mentioned U.S. patents can simultaneously measure various parameters, such as the friction torque, temperature rise, and amount of vibration, etc., but the way of applying the load on the bearings and the measurement of vibration with direct contact will interfere with the accuracy of the measurement of the friction torque. The testing apparatus disclosed in U.S. Pat. No. 5,477,730 uses acceleration signals and employs band-pass and digital filtering and envelope detecting techniques, which are vulnerable to the outside interfering signals. Therefore, the testing results of the bearing performance will not be very reliable if the outside interfering signals are not handled cautiously and appropriately. Moreover, some of the testing systems require a costly apparatus, such as a laser.
In the above-mentioned testing systems, there is a critical factor which is not considered. The testing systems are not effectively integrated with a lubricating system to evaluate the performance of the bearings under various lubrication systems. For the rolling bearings, the lubrication system has significant influence on maximum rotating speed and service life. Therefore, an ideal apparatus for testing the performance of rolling bearings should be integrated with a lubrication system that is able to test the rolling bearings under different lubrication conditions.